The problem of releasing manufactured articles and processed goods from flexible machinery components with which they may come in contact is a recurring one that arises in many varied situations. Unless it is adequately solved, undesirable adhesion of the materials or goods may hinder or even block assembly and conveyor lines. In extreme cases, the articles and goods as well as machinery can be damaged by such blockage. The problem is particularly prevalent with elastomeric structures or components such as conveyor belts and devices such as flexible diaphragms, bags, bladders, sleeves and the like which are often made of elastomeric materials such as rubber which possess natural stickiness or tack. The solution of such problems in a convenient, safe and efficient manner allows high speed manufacturing and processing operations with minimal damage and delay. The solution of such problems may be complex because some degree of adhesion is usually desirable or necessary to allow efficient functioning. If machinery components are too slick, improper positioning of components and work pieces can occur. Therefore it is optimum to have a means of controlling surface adhesion characteristics as the present invention provides.
The present invention is directed to convenient, safe, economical and expeditious means for controlling the natural surface tack or stickiness of flexible elastomeric structures and machinery components such as belts and polymeric diaphragms such as found in bags, bladders, sleeves, and the like. It comprises forming on the flexible surface which contacts the articles or goods, an exposed controlled adhesive release coating which is fracture (that is, crack) resistant. Surprisingly this surface coating or film can be formed from materials which in some cases have previously found use as components of adhesives or bonding agents, an application that is antithetical to the purpose they serve in the present invention. In one embodiment of the invention, the surface release coating is applied or formed on at least a portion of the surface (usually the outer surface) of a flexible diaphragm which, through inflation or other mechanical means, exerts pressure on a naturally sticky article such as one made of rubber. In other embodiments the invention is employed in conveyor belts and molds which contact such diverse materials such as thermoplastic articles and frozen food goods during their collection, processing and storage. For convenience and brevity, the use of the invention in the former application will be discussed in detail below. By so doing, it is to be understood that the full scope of the invention is in no way thereby limited.
Machines for the assembly of tires (TAMS) contain elastomeric structures such as inflatable rubber bladders which are conventionally used for such manufacturing operations as turning up ply ends over bead rings and against plies on the TAM mandrel or drum. These rolling, inflatable turn-up bladders (TUBS) turn the ends of the plies wrapped on the tire building mandrel up around the bead rings and over them against the ply material. The rubber ply material is tacky by nature, and it is this tack which causes the plies to stick together and thus maintain the integrity of the partially built or green tire. The TUBS are conventionally made from vulcanized rubber, natural, synthetic or mixtures of the two with optional fabric reinforcement, and the tacky ply ends have a tendancy to stick to the outer surfaces of the bladder which turn them up, particularly, since the inflated bladders exert pressure on the turned-up ply ends. This adhesion tends to retard the retraction of the deflated bladders, and it can also result in erosion of the bladder material coming in contact with the ply ends. Thus it is desirable to provide TUBs with surfaces which are non-adhesive or releasing to the tire plies with which they may come in contact. One solution to this problem is found in U.S. Pat. No. 4,381,331 to Johnson, which describes a ply turnover bladder having at least a portion of its outer surface comprising a fabric layer of spaced cords calendered with a coating of unvulcanized, uncured rubbery polymer, the spaces between the cords being free of said polymer at the surface so that the cords project above said surface. It has been found that this structure has reduced tendency to adhere to the rubber ply of tire components and thus release the tire during its manufacture. Naturally, the construction of the Johnson bladder is somewhat complex, involving several manufacturing and, particularly, finishing steps which must be carefully controlled to achieve the desired controlled adhesive surface. For this reason, Johnson bladders are expensive to make.
Another related embodiment of this invention is found in tire curing bladders having an outer releasing surface coating and in a method of curing tires utilizing such coated bladders. Conventionally, pneumatic rubber vehicle tires are produced by molding and curing a green or uncured and unshaped tire in a molding press. In the press, the green tire is pressed outwardly against the mold surface by means of an inner, fluid-expandable bladder. By this means the green tire is shaped against the outer mold surface which defines the tires tread pattern and configuration of the sidewalls. Generally, the bladder is expanded by internal pressure provided by a fluid such as hot gas, hot water, and/or steam. The use of such tire curing bladders is well known in the art of tire manufacture. It is also known that difficulties may occur between the bladder and the inner surface of the tire if there is excessive adhesion, that is, the lack of release between the two. Typically, this results in deterioration of the bladder, misshaping of the tire in the mold, and similar problems. Furthermore, air bubbles can potentially become trapped between the bladder and tire surfaces and promote tire vulcanization defects. For this reason, it is conventional practice to precoat the inner surface of the green or uncured tire with a lubricant in order to provide lubricity between the outer bladder surface and the inner tire surface. Such lubricants have sometimes been called lining cements, band ply dopes and bag dopes. Conventionally, the inner surface of the green tire, which is typically a rubber gum stock, is simply spray coated in a combined ventilated spray booth with a lubricant which might, for example, be based on silicone polymers. Other additives may also be conventionally utilized in this application, such as mica, polymeric materials, polyols, polyethers, clays, and the like. Another approach to this problem is the alternative of coating the bladder itself. One such example of a tire curing bladder lubricant is found in U.S. Pat. No. 4,359,340, to Comper, et al, which describes an aqueous lubricating composition for tire curing bladders containing polydimethylsiloxane, a silane, a surfactant and, optionally, a metal salt of an organic acid.
Still another means of solving the problem of undesirable adhesion between tacky tire plies and similar elements and flexible TAM components such as bladders and sleeves is the so-called Red Release coat developed by The Firestone Tire & Rubber Company. This coat consists of a polymeric film formed from a fluxed (that is, heat-treated) blend of PVC and a copolymer of butadiene and acrylonitrile (for example, Paracril OZO). This material is available as a thin sheet that is cemented to the bladder or sleeve on which the release coating is desired. The red release coating can be subject to cracking during use. Such cracks have been found to propagate into the flexible underlying elastomeric structure and thus cause premature failure of the component. One of the cements used in adhering the red release coat to flexible diaphragms such as bladders, sleeves, bags and the like is Chemlok-234B, which is described in more detail below.